Conventional articles of footwear include two primary elements, an upper and a separate sole structure. The upper may provide a covering for the foot that securely receives and positions the foot with respect to the sole structure. The sole structure is secured to a lower portion of the upper and is generally positioned between the foot and the ground. In addition to attenuating ground reaction forces, the sole structure may provide traction, control potentially harmful foot motion, and support the bottom of the foot and the arch. The upper and the sole structure should cooperatively provide a comfortable structure that is suited for a wide variety of ambulatory activities, such as walking and running.
The upper forms a void on the interior of the footwear for receiving the foot. The void has the general shape of the foot, and access to the void may be provided by an ankle opening. The upper typically extends over the instep and toe areas of the foot, along the medial and lateral sides of the foot, and around the heel area of the foot. A lacing system is often incorporated into the upper to selectively increase the size of the ankle opening and permit the wearer to modify certain dimensions of the upper, particularly girth, to accommodate feet with varying proportions. In addition, the upper may include a tongue that extends under the lacing system to enhance the comfort of the footwear, and the upper may include a heel counter to limit movement of the heel.
The sole structure of conventional articles of footwear may incorporate multiple layers that are conventionally referred to as an insole, a midsole, and an outsole. The insole may be a thin, comfort-enhancing member located within the upper and adjacent the plantar (lower) surface of the foot to enhance footwear comfort. The midsole, which is traditionally attached to the upper along the entire length of the upper, forms the middle layer of the sole structure and may serve a variety of purposes such as control of foot motions and attenuation of ground reaction forces. The outsole may form the ground-contacting element of footwear and can be fashioned from a durable, wear-resistant material that includes texturing to improve traction.